Introduction

The activity of large vessel vasculitis is usually assessed by a segmental approach by using FDG-PET/CT¹. The advantage of FDG-PET/CT is its well-documented clinical usefulness, but its disadvantages include limited applicability to diseases and conditions, high cost, and radiation exposure. The possible advantages of DWI over FDG-PET are that the signal and morphology of the arterial wall can be assessed unencumbered by the signal of the vessel lumen, the combination with anatomical MRI such as T2-weighted images or balanced turbo field-echo can provide a lot of histological information, and the cost is lower. However, one of the problems with DWI is that the depiction of the ascending aorta is reduced by the effect of the heartbeat. The acceleration motion compensation diffusion-weighted imaging (aMC-DWI) may visualize the ascending aorta and allow clinicians to use MRI for diagnosis and monitoring of disease activity of large vessel vasculitis. The purpose of this study was to investigate whether aMC-DWI could be an alternative to FDG-PET/CT for the detection of ascending aortitis.

Methods

A phantom experiment and a clinical study were conducted on a 1.5 T MRI scanner. Qualitative comparisons were made between the aMC-DWI and conventional DWI (cDWI) (b factor=800 s/mm² for both) since the apparent diffusion coefficient value of aMC-DWI could not be acquired in principle. The phantom was comprised of a syringe (internal diameter 9 mm), which was filled with agar, attached to a balloon. Two experimenters independently manipulated the balloon to move the syringe up and down in 5 mm range at 60 times per minute. Twenty image slices obtained over four sessions (two experimenters/two DWI techniques) were graded on a 5-point scale (1=poor to 5=as good as a static image by using cDWI). Mann-Whitney U tests with Bonferroni correction were used to assess differences among the sessions. The prospective clinical study was performed on patients with suspected aortitis undergoing DWI using both two techniques. cDWI and aMC-DWI were visually scored for active inflammation of the ascending aorta (0=negative or 1=positive), and the difference value (aMC-DWI - cDWI) was calculated for each patient. We compared the detectability of inflammation in the ascending, arch, and descending portions of the thoracic aorta between the two DWI techniques using FDG-PET/CT as the reference method. Statistical analyses included calculation of sensitivity, specificity, and positive and negative predictive value (PPV and NPV, respectively), as well as a two-sided one-sample t-test (assuming mean difference = 0).

Results

In the phantom experiment, aMC-DWI showed a significantly higher median score than cDWI in both experimenter 1 (4 vs 3; P =.048) and experimenter 2 (3 vs 1; P =.048). In the clinical evaluation, 11 patients (median age, 37 years [range, 19-84 years]; 10 women) were assessed. Five patients were diagnosed as aortitis (two with giant cell arteritis and the other with Takayasu arteritis) and FDG-PET/CT indicated active inflammation in the ascending aorta in four patients (maximum standardized uptake value range, 3.2 and 4.4). The sensitivity, specificity, and PPV and NPV, respectively, for detecting active inflammation in the ascending aorta (with FDG-PET/CT as the reference method) were 0/4 (0 %), 7/7 (100 %), 0/0 (Inf), and 7/11(64 %) for cDWI; and 4/4 (100 %), 6/7 (86 %), 4/5 (80 %) and 6/6 (100%) for aMC-DWI. The one sample t-test revealed a significant difference between two DWI techniques (t = 2.887; P = .016; 95% CI = 0.10 – 0.81).

Conclusion

The acceleration motion compensation DWI improves aortic delineation over conventional DWI and promises to increase the utility of MRI in assessing activity and extent of large vessel vasculitis.

Acknowledgements

Not applicable

References

1. Slart R, Writing g, Reviewer g, et al. FDG-PET/CT(A) imaging in large vessel vasculitis and polymyalgia rheumatica: joint procedural recommendation of the EANM, SNMMI, and the PET Interest Group (PIG), and endorsed by the ASNC. Eur J Nucl Med Mol Imaging. 2018;45:1250-1269.